Dairy Cow Heat Detection

New University of Wisconsin research has concluded that your chances
of success for detecting heat in high-producing cows is just over
half the rate for average milking animals. If you routinely check
for heat only once or twice per day, your success rate drops even
more.

Wisconsin researchers report that high-producing cows are in estrus
for a shorter period of time than lower producing herdmates. A regular,
frequent heat detection routine could detect standing heats more
successfully.

Heat detection is basic to reproductive success in artificially
bred dairy herds, yet estrus detection rates have decreased in recent
years. A study of southeastern U.S. Holstein herds, for example,
showed heat detection rates dropped to 41.5 per cent in 1999 from
50.9 per cent in 1985.

Reduced heat detection success tends to be blamed on increased
herd sizes and more cows per person, as well as higher milk production
per cow.

Part of the negative relationship between fertility and high milk
production may be genetic. However, the genetic component in cow
fertility performance tends to be small.

This leads to the question of whether shorter estrus durations
make heats more difficult to detect. Dr. Milo Wiltbank and associates
in Wisconsin studied lactating dairy cows to measure duration. They
used the HeatWatch system that fits cows with radio transmitters,
and allows continuous monitoring and recording of mounting activity.

The study monitored 267 early-lactation cows housed in a free-stall
barn and milked twice daily. The HeatWatch system let researchers
record number of mounts and how often they occurred. They checked
ovulation by ultrasonic exam for all detected estruses.

Researchers made comparisons according to lactation number, days
since calving, and the amount of milk given 10 days before the day
of estrus. That let them make sure the production level was linked
closely to when the estrus occurred, not overall lactation milk.

When the cows were grouped according to high and low production,
estrus duration [standing to be mounted] was shorter for the high-production
group, the researchers found. This group, averaging 46.4 kilograms
of milk per day, were in estrus 6.2 hours on average, compared with
the lower production group at 10.9 hours.

There was a negative correlation between milk production and estrus
duration. The high group had more intense mounting activity, with
more mounts during the shorter time period. Still, the lower production
group averaged 8.8 mounts versus 6.3 for the high-producing group.

Some interesting and challenging information about estrus events
revealed by this study included:

15 per cent of recorded estruses consisted of only one standing
event;

estruses with recorded standing events-two or more-were detected
on average 93 days after calving, with a range of 50 days when
heat detection didn't start until 165 days;

average duration was 8.7 hours, with an average of 7.6 standing
events;

standing events lasted only 25 seconds per estrus on average.

On the first ovulation 50 days after calving, the HeatWatch system
detected no standing activity among 41 per cent of the cows, and
only one standing event among 52.6 per cent. Cows that showed no
standing activity had higher production.

Many theories have been put forward to explain why high-producing
cows have poorer fertility. Wiltbank's study provides another one.
He and his team measured circulating levels of reproductive hormones
in the cows and found that high-producing animals tended to have
lower levels of estradiol and progesterone. Estradiol affects how
well a cow shows heat signs. Circulating progesterone levels tend
to be low in high-producing cows as well, although their ovaries
tend to have higher-than-average amounts of progesterone-producing
luteal tissue.

Modelling done as part of this research showed high-producing cows
metabolize more estradiol and progesterone through their livers.
Since this removes reproductive hormones from circulation more quickly,
they are less available to do their job. It could explain the reduced
estrus activity.

Wiltbank used the data from this study to predict the probability
of successfully detecting standing heat in a cow based on her milk
production. With four-times-per-day heat detection, the probability
of success is about 90 per cent for cows producing about 35 kilograms
of milk per day. For cows producing 45 kg per day, the success rate
drops to 50 per cent probability, and results are even poorer when
heat detection is carried out just once or twice a day.

It is also interesting to note in this study that cows exhibited
recordable standing behaviour at 93 to 95 days after calving on
average. This suggests your breeding program may be more successful
if you intensify heat detection and breeding between 95 and 120
days.

Recent CanWestDHI data indicate this practice doesn't harm overall
profit. An important consideration in managing lactation and calving
intervals is to maintain the dry interval at 40 to 70 days. A dry
period longer than 70 days has been shown to reduce overall production.

Other considerations for successful heat detection include:

frequent, regularly timed observation of high producing cows.
Bear in mind that cows may only show standing heat for four to
six hours and actual standing events may last 25 seconds in total;

choosing times when and places where cows tend to exhibit mounting
behaviour;

using records to advantage to help identify cows most likely
to be in heat;

using timed insemination to supplement a heat detection program
or replace it entirely;

reviewing when you begin breeding cows for the first time after
calving and when you have the most success. Delaying breeding
by a cycle combined with an efficient program to heat detect and
breed cows may be more efficient.

On many dairy farms, spring and early summer put heavy demands
on your time, giving you less opportunity to spend on routine milking
herd management. Re-examine your procedures and change them as needed
to ensure the best odds of successful heat detection.

Site Help

Notices

Accessing this message means you do not have a JavaScript enabled browser. If you
cannot enable JavaScript in your browser and would like to know the last modified
date for this page, please contact the webmaster at -internet.webmaster.omafra@ontario.ca